How do I go about this?

[JohnW2]

Yep, i`ll not disagree with that John, in essence. ... What I was attempting was , what is the best (easiest) way to refer to them in comparison, loosley we calls the current operated (RCD like, comparing currents) or voltage operated (comparing voltages) as a ready distinguishable different kind of "Earth Leakage Circuit Breaker" as we used to call them .....

Yes, I understand and respect the argument you are attempting to present. However, as I've said, I'm really not sure that it is particularly meaningful/useful to call one 'current-operated' ('current comparing') and the other 'voltage-operated' ('voltage comparing') - since both will operate when a certain current flows through them - which, again in both cases, could alternatively be expressed as the voltage across them required for a trip.

- but we changed that because they never did measure earth leakage they (both) compared either voltages or currents and made their conclusion.

As above, when only 'passive'components'(device coils in this case) are involved, current and voltage are directly, and linearly, related to one another, so one can express the 'trip threshold' as either a current or a voltage (in both cases).

In fact, neither of the technologies (OPDs or RCDs) we currently use for 'fault protection' actually look at 'earth leakage. OPDs only trip in response to the massive current (in L) resulting from a L-E fault 'of negligible impedance', whereas, as you know, an RCD just looks at the L-N current difference and trips if that difference exceeds a certain value. However, in neither case is there any certainty that a trip has resulted from 'earth leakage' - an OPD obviously may operate in response to an L-N fault, and an RCD may operate as a result of a connection or fault to another circuit.

It became apperent that in some instances the "voltage operated" devices could more often make the wrong conclusion under some circumstances, therfore the current operated devices where the more fit for purpose of those two types.

Yes, probably - although, as above an RCD can operate as a result of a fault (or erroneous connection) to the L or N of another circuit, without any 'earth leakage' being involved.

Of the two we've been discussing (RCD and VOELCB), I would have said that the VOELB is the 'closer' to actually looking at 'earth leakage' - although, as I've said, it will 'miss' any earth leakage going through a 'parallel path' (rather than going to the installation's 'earth').

Indeed the Current Operated Types (RCD etc) do not actually need an earth reference to be present to detect that problem in some instances in order to be able to "see and disconnect" in the case of a fault.

Quite so - but, as above, that makes them a bit less 'pure', since they can sometimes operate in response to situations which involve no 'earth leakage'.

So it`s just a case of the best easy name of the devices to differentiate their operation and therefore the inherent advantages of one versus the other rather than the fully correct explanation of their method of operation.

Yes, I understand that but, as I keep saying, I'm not convinced that,'technologically', there's as much difference in their 'methods of operation' as you seem to be implying. Both trip if the current through them is greater than some threshold (or, if you prefer, when the voltage across them is greater than some threshold) - and it would, today, be possible to make a 'VOELCB' which was as 'sensitive' as an RCD. I suppose that the main difference of practical importance is that the VOELCB will miss 'earth leakage' which goes to earth via parallel paths (possibly through a human being) - but it is also true that an RCD (but not VOELCB) can, in some situations, trip for reasons other than 'earth leakage'. 'Horses for courses', I suppose

Kind Regards, John

 

[ericmark]

I would have said that the VOELB is the 'closer' to actually looking at 'earth leakage'

OK pedantic rules KO, yes the ELCB-v measured the voltage and hence current flowing between the bonding in the building and the true earth, so be it voltage or current, it is measuring earth leakage not live differential current.

We traditionally called a high impedance or resistance measuring device a volt meter/sensor, and a low impedance or resistance measuring device an amp meter/sensor.

Except for the valve volt meter or comparator we would draw power from the circuit and how much power was referred to as ohms per volt. I think the AVO Mk8 was around 20k ohms per volt. Still have one, but not used in years.

 

[JohnW2]

OK pedantic rules KO, yes the ELCB-v measured the voltage and hence current flowing between the bonding in the building and the true earth, so be it voltage or current, it is measuring earth leakage not live differential current.

It certainly is operated by 'earth leakage' (provided the leakage path is through the earthing conductor) rather than differential current but, as I've said, one can express the trip threshold as either a current or voltage.

We traditionally called a high impedance or resistance measuring device a volt meter/sensor, and a low impedance or resistance measuring device an amp meter/sensor.

Although I suppose it is in some senses true, that seems to be a rather odd statement. The main reason why it is true is that if one did the opposite (tried to measure/sense voltage with a low resistance/impedance device, or to measure/sense current with a high resistance/impedance device) one could seriously (and possibly dangerously) affect the circuit one was looking at (and thereby invalidating the results one observed).

Except for the valve volt meter or comparator we would draw power from the circuit and how much power was referred to as ohms per volt. I think the AVO Mk8 was around 20k ohms per volt. Still have one, but not used in years.

True, but I'm not sure what that has got to do with this discussion. "20kΩ per volt" in a traditional meter was merely a way of indicating that the actual 'meter' had a 0-50 μA movement.